The present invention relates to a control apparatus for use of a continuously variable transmission, and more particularly to an apparatus for controlling a speed ratio between an input pulley and an output pulley of a continuously variable transmission.
There has been known a continuously variable transmission (CVT) comprising a torque transmitting belt extending between an input (driving) pulley and an output (driven) pulley, the ratio capable of being varied (ratio being defined as the RPM or speed ratio between the input and output pulleys), by adjusting the size of a V-shaped groove(s) in one or both of the pulleys as a result of the variation of the pressure which forces the belt into groove(s). Thus, the position of the belt on the pulleys and the effective diameter of the pulleys can be varied, which makes it possible to continuously vary the ratio between the input and output pulleys.
In a vehicle equipped with a CVT, a desired engine speed is set to such a value as a required horsepower is obtained at a minimum fuel consumption, and a speed ratio e of a CVT (e=RPM.sub.out /RPM.sub.in, RPM.sub.out : a rotation speed of a driven pulley, RPM.sub.in : a rotation speed of a driving pulley) is controlled by hydraulic cylinders so that an actual engine speed may become equal to a desired engine speed. Hence, an engine speed of a vehicle in which a CVT is equipped, is made to a smaller value than that of a vehicle in which a manual transmission or an automatic transmission is equipped. Even in a vehicle in which a CVT is equipped, it is necessitated to promptly increase an engine speed when a prompt acceleration of a vehicle is required. When a time for changing a speed ratio of a CVT lasts for a long time, the increased engine torque is used mostly in order to further increase an engine speed.